Oxy-fuel burners in furnace tuyeres

ABSTRACT

Industrial furnaces for processing metal bearing charge in which a plurality of oxy-fuel burners are interposed through the walls of the furnace to direct high velocity streams of oxygen and hydrocarbon fuel into the hearth portion of the furnace. Each of the burners comprising a plurality of separate channels for high velocity streams of commercially pure oxygen and hydrocarbon fluid fuel, said channels terminating in a nozzle constructed to emit a plurality of high velocity jets of oxygen surrounding at least one jet of hydrocarbon fuel.

United States Patent Gray [54] OXY-FUEL BURNERS IN FURNACE TUYERES [72]Inventor: Bronh G. Gray, Orange, NJ.

[73] Assignce: Airco, Inc., New York, NY.

[22] Filed: Aug. 7, 1970 [21] Appl. No; 62,180

Related US. Application Data [62] Division of Ser. No. 602,381, Dec. 16,1966,

Pat. No. 3,547,624.

1 Oct.3l, 1972 3,089,766 5/1963 DeWald ..75/43 3,213,918 10/1965 Rudzkiet al............239/l32.3 3,224,679 12/1965 Kear et a1. ..239/ 1 32.33,236,281 2/1966 Bain et a1 ..239/ 132.3 3,266,552 8/1966 Denis..239l132.3 3,317,309 5/ 1967 Rinesch ..75/43 3,366,469 1/ 1968 Kedamaet a1 ..266/29 Primary ExaminerGera1d A. Dost Attorney-Edmund W. Boppand H. Hume Mathews ABSTRACT industrial furnaces for processing metalbearing charge in which a plurality of oxy-fuel burners are interposedthrough the walls of the furnace to direct high velocity streams ofoxygen and hydrocarbon fuel into the hearth portion of the furnace. Eachof the burners comprising a plurality of separate channels for highvelocity streams of commercially pure oxygen and hydrocarbon fluid fuel,said channels terminating in a nozzle constructed to emit a plurality ofhigh velocity jets of oxygen surrounding at least one jet of hydrocarbonfuel.

8 Claim, 25 Drawing Figures OXVGEN -FUEL SUPPLV SYSTEM WATER PUMPINGSYSTEM PATENTED B 2 3 701 517 sum 01 or 16 FIG.

OXYGEN -FUEL SUPPLY SYSTEM WATER PUMPING SYSTEM PKTENTED B I9733,701,517

sum new 16 BURNER COOLING WATER INLETS 35 PATENTEU nm a 1 m2 SHEET DBBF16 PAIENTEDucI 31 1912 3.701 51 T sum near 16 PATENTED um 31 m2 sum DSUF16 FIG. 9

32 OXY-GAS BURNERS 3o CALCULATED III-OBSERVED I.51IOXY-FUEL RATIO (BYVOLUME) 28 OBSERVED 2:!

OXY'FUEL RATIO O 7 M24 d g LL 22 CALCULATED 0, g EFFECTIVE 0 520 O E43.6% I6 GFEUWE E 3 as M EFFECTIVE OllilllllllllllL NATURAL GAS FLOW PERTUYERE- SCFH I00 PATENTEDBBT 31 m2 MELTING RATE N0.0F 5000 LB.CHARGESMELTED PER HOUR SHEET llUF 16 X-CALCULATED O-OBSERVED LSII zOXY-FUELRATIO OXY- GAS BURNERS AVERAGE LINE NO BURNERS l l l 1 l l l WINDRATE-SCFM I000 P'ATENIED um 31 I972 FREQUENCY- PER CENT A G) FREQUENCY-PER. CENT a m SIIEEI' 120T 16 DISTRIBUTION OF SPOUT TEMPERATURES NORMALOPERATION I44 OBSERVATIONS MEAN2903F.

SPOUT TEMP. DE

FIG. /.3B

DISTRIBUTION OF SPOUT TEMPERATURES OXYGEN-OIL BURNER USE I00OBSERVATIONS MEAN|2920E 4% I 4| 8 I3 Z5I I SPOUT TEMP DEGF.

PATENTEDncm 1912 3.701 517 sum 13 0F 16 OXYGEN-FUEL SUPPLY SYSTEM WATERPUMPING SYSTEM FIG. /5

OXYGEN FUEL PNENTEDum 31 m2 SHEET lSUF 16 FIG. /7

FIG. [8

OXY-FUEL BURNERS IN FURNACE 'I'UYERES CROSS REFERENCE TO RELATEDAPPLICATION This is a Division of copending application Ser. No.602,381, filed Dec. 16, 1966 for OXY-FUEL BUR- NERS IN FURNACE TUYERESand now US. Pat. No. 3,547,624.

This invention relates in general to industrial melting and smeltingprocesses and apparatus, and more particularly to techniques andarrangements for using tuyere burners in various types of shaft furnacesfor processing metals.

ln melting iron and steel in cupolas, and smelting ore containing ironand other metals in blast furnaces, the economics of the processes andthe quality of their products are functions of the rates andtemperatures of the melting and smelting operations.

The cupola, for example, is designed to melt pig iron and steel scrap,using coke as fuel, to produce molten castings. Changes in the meltingrate, temperature, and composition of the product can be made by propermanipulation of the charge, fuel, and air blast.

in the prior art, various attempts have been made to reduce theconsumption of coke and to increase the proportion of steel scrap usedin place of more expensive pig iron in the charge by supplying low costunits of heat directly to the combustion area of the furnace, by theexpedient of placing burners in the furnace tuyeres. The use of burnersin the prior art manner has been only partially successful, inasmuch asthese burners are designed to operate with relatively low velocityflames sustained by air, or slightly enriched air, containinginsufficient oxygen to effect a complete combustion of the burner fuelin an established combustion zone in the burner tuyere. A particulardisadvantage of such an arrangement is that a substantial amount ofnitrogen remains after the combustion, in addition to certain undesiredcombustion products, including water vapor, which cool the flame andcarry combustion heat up the stack. Another disadvantage of prior arttuyere burner arrangements is that the combustion products are notproperly mixed before entering the furnace, thereby producing an uneven,unpredictable effect on the melting or smelting processes. A furtherdisadvantage is that after shutdown or in starting up, the temperatureand melting rate in the furnace increases very slowly. Anotherdisadvantage in the prior art operation of melting and smeltingprocesses is that the temperature in the furnace is often insufficientto prevent the formation of what are known in the art as bridges" andskulls," the former arising when pieces of scrap become fused in thecupola stack and the latter arising when molten metallics solidify andform accretions within the shaft.

Accordingly, it is a general object of the present invention to improvethe melting of iron, steel, and other metals or smelting their ores inshafl furnaces by substantially increasing the rate at which charge isconsumed, and substantially increasing the metal or ore-tocoke ratio.

A more particular object of the present invention is to increase themelting or smelting rate and to increase the temperature in the furnace.

Another object is to provide techniques and apparatus which require theuse of less expensive charge materials, such as steel scrap instead ofpig iron and silicon dioxide in place of higher priced silicon alloys.

Another object of the invention is to improve the chemical compositionof the product, and render the same subject to more exact control, byincreasing the uniformity and predictability of the process.

Other objects of the invention are to increase the slag fluidity anddecrease the tendency for the formation of bridges and skulls in thefurnace.

These and other objects are realized in improved techniques andapparatus for melting and smelting iron and other metals in accordancewith the present invention in a shaft furnace having a plurality oftuyeres adjacent the hearth portion which are equipped with inwardlydirected oxy-fuel burners. A salient feature of the tuyere burners ofthe present invention is that combustion takes place in an establishedcombustion zone in the tuyeres, in the form of a single, homogeneous,coherent, high velocity, high temperature flame adjacent to or seated atthe end of the burner which creates a high degree of turbulence insideof the tuyeres mixing the combustion products into a substantiallyhomogeneous stream.

These burners are supplied with streams of fuel comprising hydrocarbonfluid surrounded with high velocity streams of commercially pure oxygen,the latter at a mass flow rate of from one-quarter to twice thestoichiometric requirement for complete combustion of the fuel.Together, these streams produce flames having temperatures of from 3,000to 5,000 F. and flames velocities within the range 500 to 3,500 feet persecond, which flames are adapted to remain seated in the mouth of theburner, conforming to an established combustion zone in the tuyere.notwithstanding the presence of inwardly directed, surrounding airblasts having velocities of between 150 and 1,000 feet per second in thetuyere. In these cases where combustion is well established withineither the burner or the tuyere, flame velocity is defined as thearithmetic mean of the oxygen and fuel free stream velocities measuredin the plane of the inner end of the tuyere.

In one specific embodiment of the invention described hereinafter, whichrelates to the making of molten iron in a cupola, a plurality of furnacetuyeres were equipped with oxy-oil water-cooled burners comprisingself-atornizing tip mixers. These were supplied with streams of fuel oil(A.S.T.M. grade 2) and high velocity streams of commercially pureoxygen, the latter in an amount representing 65 percent or more of thestoichiometric requirement for complete combustion of the oil. Thesearrangements produced a single coherent homogeneous flame in each of theburner tuyeres having flame velocities of between 500 and 1,500 feet persecond, and flame temperatures within the range 4,000 to 5,000 E, whichwere stable in wind velocities up to 500 feet per second flowing throughthe tuyeres. Under these arrangements the melting rate of chargesupplied to the cupola was increased percent. The burner tips werewithdrawn from the ends of the tuyeres so that complete combustion tookplace in an established combustion zone in each of the tuyeres.

In another embodiment in accordance with the invention, water cooledrocket burners were employed in the tuyeres of the iron melting cupola.These latter butners were supplied with commercially pure oxygen andnatural gas, having a heating value of approximately L000 Britishthermal units per cubic foot, at an my fuel ratio of 1.5:1, the oxygenbeing 75 percent of the stoichiometric requirement for completecombustion of the natural gas fuel. This embodiment is alsocharacterized in each burner by a homogeneous high velocity seatedflame, notwithstanding high wind velocities, and showed an increase overprior art techniques in the melting rate of the charges supplied to thecupola, which was a substantial improvement over the prior art, althoughless pronounced than that achieved with oil fuel.

In accordance with additional modifications disclosed hereinafter, theprincipals of the invention are also applied to the smelting of orescomprising a principal component of iron and other metals, such ascopper, lead, and antimony, in blast furnaces wherein burners, also of ahigh-velocity flame type, are installed for these applications in thefurnace tuyeres or at the level of the combustion zone in the furnace.In each case, a single high velocity, high temperature oxy-fuel flame isemployed, total combustion taking place in an established zone in thetuyere, or furnace barrel.

The particular advantages to be derived from em ploying oxy-fuel furnaceburners with homogeneous high velocity coherent flames in melting andsmelting furnaces in the manner disclosed in detail in the specificationhereinafter and the attached drawings are:

1. Higher metal temperatures are produced; and the melting rate isincreased.

2. The uniformity and predictability of the process is increased.

3. The coke consumption in the furnace is decreased.

4. More economical types of charge can be employed in the processes. Forexample, in the 8"cupola, scrap steel can readily be substituted formore expensive pig iron, and silicon dioxide substituted for moreexpensive silicon alloys.

5. The product is improved and the composition is more readilycontrolled. In the iron melting cupola, for example, the carbon pick-upis increased, whereas the sulfur pick-up is decreased, and silicon andmanganese losses are decreased. In the smelting process, the chemicalcomposition of the combustion products of the burner flame can becarefully controlled to facilitate the reduction process.

. The actual functioning of the furnaces is improved by increased slagfluidity and lessened tendency for the formation of bridges" and"skulls.

These and other objects, features, and advantages will be apparent tothose skilled in the art from a study of the detailed specificationshereinafter with reference to the attached drawings, in which:

FIG. 1 shows, partly in sectioned front elevation and partly inschematic, a system including an iron melting cupola modified to includeoxy-fuel burners in accordance with the present invention;

FIG. 2 shows in enlarged longitudinal section the location of anoxy-fuel burner in one of the tuyeres of the cupola of FIG. 1;

FIGS. 3A and 3B show, in longitudinal section and in cross sectionrespectively, a self-atomizing tip mixer type of oxy-oil burner for usein accordance with the present invention;

FIG. 4 shows, in enlarged perspective, details of the oxy-fuel and watersupply lines in the system of FIG. 1;

FIG. 5 shows an oxygen-oil supply system for the oxy-oil tuyere burnersystem of FIGS. 3A, 38;

FIGS. 6A and 6B show an oxy-gas rocket burner insert for modification ofthe burner combination shown in FIGS. 3A, 38;

FIG. 7 shows an oxygen-gas supply system for use with a burner employingan insert of the type shown in FIGS. 6A, 68;

FIGS. 8A and 8B, combined along their lines x-x, show in longitudinalsection an oxygen-fuel rocket burner for alternative employment in thearrangements of FIG. I of the present invention;

FIG. 8C is a cross sectional showing of the burner of FIGS. 6A, 68;

FIG. 9 shows the relation between observed wind heating by an oxy-gasburner in a tuyere and calculated values;

FIG. 10 shows a plot of melting rate as measured by charges consumed perhour versus wind rate for a eupols operating without burners inaccordance with prior art practice;

FIG. 11 shows a similar plot of melting rate versus wind rate for acupola operating with oxyfuel burners in accordance with the presentinvention, employing high gas flows;

FIG. 12 shows a similar plot of melting rate versus wind rate for acupola operating with oxy-oil burners in accordance with the presentinvention;

FIGS. [3A and 13B are a comparison of the distributions of spouttemperatures for normal operation of a cupola and operation includingoxy-oil burners in accordance with the present invention;

FIG. 14 shows, partly in front elevation and partly in schematic, asystem including an iron ore smelting blast furnace modified to includeoxy-fuel burners in accordance with the present invention;

FIG. 15 shows in enlarged cross section a tuyere and surrounding area inthe blast furnace of FIG. 14, indicating the oxy-fuel burner location inaccordance with the present invention;

FIG. 16 shows, partly in longitudinal section and partly in schematic, arectangular blast furnace, suitable for the smelting of ore containinglead or antimony, including oxy-fuel burners in accordance with thepresent invention;

FIG. 17 shows in plan view the location of the tuyere burners in thelead blast furnace of FIG. 16;

FIG. 18 shows, in enlarged long'tudinal section, the location of anoxy-fuel burner in one of the tuyeres of the lead blast furnace of FIG.16; and

FIGS. 19A, 198 show, in longitudinal section and cross-section,respectively, typical rocket burners suitable for use in the tuyeres ofthe lead blast furnace of FIG. 16.

Referring to FIG. I of the drawings, there is shown a conventional hotblast iron melting cupola I (water jacket not shown) which is one of thetypes of furnaces suitable for application of the oxy-fuel tuyereburners in the manner of the present invention.

The specific cupola shown for purposes of the present illustrationcomprises a cylindrical steel shell 2, which is inches in outerdiameter. The shell 2 consists of heavy steel plates, rolled intocylindrical sections, and riveted, bolted, or welded together withdownwardly lapping joints. The top of the stack 2 is reinforced with anangle-iron ring 3, which is riveted on in such a manner as to affordprotection against rain seepage between the lining and the shell. Thetop of the stack generally extends to a minimum of feet above the roofof the foundry and is sometimes carried further to provide foradditional natural draft at the charging opening, or to provideadditional space to permit complete combustion of the gases above thecharged column. The angle-iron 3 supports a plurality of upwardlyextending rods on which are mounted a conventional slant-roofed,perforated spark arrestor 5, which has an external annular opening 40, afoot or so high, at the bottom, and a smaller annular opening 4b in theupper portion, for release of smoke and exhaust gases.

The lower, or body, section of the cupola is supported by four columns6, about 8 feet high, mounted on a concrete foundation 7. The lowersection is sub stantially constructed to give proper support to the loadof the upper sections, since the total weight may be of the order of136,000 pounds, or more, for a cupola, say, 45 feet high. Shelf segmentsare bolted to the inside of the shell 2 at regularly spaced intervalsfor supporting a lining 8, about nine inches thick of fire-brick, in theillustrative acid-lined" embodiment.

The cast iron bottom of the cupola, which in the present embodiment is 8feet above the foundation level, is equipped with a pair of hinged dropdoors 9a, 9b, which are used for removing coke from the cupola after themolten iron has been drained from it.

Fuel is supplied to the cupola 1 through a charging door 18, covering arectangular opening in the cupola wall 2, roughly 7 feet by 10 feet, thebottom of which is located at a height of about 35 feet above thefoundation level. Just below the level of charging door 18, the cupolais surrounded by a platform 17 for facility in charging the furnace.

Layers of fuel, such as coke, and iron bearing charge, such as scrapsteel or pig iron, are fed into the furnace through charging door 18,forming alternate layers of coke and charge, the coke layer beingapproximately half the thickness of the metallic charges, to a level ofabout 27 feet above the foundation level of the cupola.

The hot gases rising in the cupola from combustion of the coke tend tomelt the iron in the charge, which trickles down through the cupola andis withdrawn through a downwardly inclined spout 19, located about 10feet above the foundation. Slag, which floats on top of the molten iron,is drawn off through slag spout 21, located at a level about 1 1 feetabove the foundation of the cupola.

Surrounding the lower end of the cupola l, at a level about 18 feetabove the foundation, is an annular pipe of rectangular cross sectionknown as the wind box 11, which in the present example is 180 inches inouter diameter, I20 inches in inner diameter, and 36 inches high. Windbox 11 is connected through an external conduit 12 to a conventionalcentrifugal blower 13,, which is designed to furnish a continuous blastof air. In the present illustration a heating unit 130 is interconnectedwith conduit 13, for heating the blast up to a temperature of aboutl,200 F., although it will be apparent that in other examples, otherarrangements are contemplated, such as the use of blasts of lowertemperatures, or cold blasts, or in some cases, no blast at all.

The blast of air carried in wind box 11 is admitted to the lower or bodyportion of the cupola through a plurality of tuyere openings 14, whichmay vary in size, shape and number from one iron melting cupola toanother. In the example under description, tuyeres 14 are eight innumber, and are symmetrically distributed around the circumference ofthe cupola wall at a horizontal level which is roughly 5 feet above thehearth level. Tuyeres 14 are cylindrical in form, having an innerdiameter of 6 inches, are 30 inches long, and are downwardly inclinedfrom the horizontal at an angle of roughly 12, as will be indicated ingreater detail in the enlarged cross-sectional showing of FIG. 2. Eachtuyere opening 14 is lined with a tuyere waterjacket pipe of copper,which is 30 inches long, 1 1 inches in outer diameter, and inch thick.The pipe 14a concentrically surrounds an inner pipe 14b of copper, 7inches in outer diameter and A inch thick. The two pipes 14a, 14b arewelded or sealed together at their inner ends, and have a radial spacingbetween them of 2 inches, to accommodate water cooling of the tuyerepassing in through a conventional water cooling system, entering andleaving the jacket through pipes 23a, 23b.

The end of the water jacket 14a, 14b of the tuyere pipe protrudes anaxial distance of 16 inches from the inner face of the cupola wall intothe interior of the cupola. The water jacket 140, which has an overalllength of about 34 inches, protrudes axially 16 inches from the outerface of the cupola wall, and terminates in an annular flange 15, towhich is bolted the matching flange 21 at the inner end of tuyereextension pipe 24.

Flange 21 is l9 inches in outer diameter, about 6% inches in innerdiameter and is inch thick. It is sealed to flange 15 against a smallintervening gasket 15a, by means of a plurality of bolts 22. Steelextension pipe 24, which has an inner diameter of 6 inches and an outerdiameter of 6% inches, extends outwardly from the junction of theflanges an overall distance of about 38 inches, so that the totaloutward-extending length from the inner end of the tuyere water jacket14a, 14b to the outer end of pipe 24 is about 6 feet. Pipe 24 protrudesabout 52 inches from the outer wall of the cupola. Centered about 2iinches inches from the outer end of pipe 24 is a downcomer arm 240,about 6 inches in inner diameter and 6 inches in outer diameter whichexecutes a half circle, and passes up through a flexible expansion joint(not shown) to make connection to wind box 11 overhead.

In accordance with the present invention, in order to expedite the ironmelting process in the cupola l, and to supply more units of heatdirectly to the combustion area in substitution for bulky units of cokeadded through the charging door, oxy-fuel burners 10 are inserted intoseven of the eight cupola tuyeres 14. These burners are each designed togenerate a single, homogeneous, coherent, seated flame, having a flamevelocity within the range of 500 to 3,500 feet per second, whichproduces flame temperatures within the range 4,000 to 5,000 F.,notwithstanding the presence in the tuyere pipes 24 of inwardly directedair blasts of between and 500 feet per second.

FIG. 2 shows, in enlarged section, one of the cupola tuyeres 14,including the tuyere extension pipe 24, and showing the position of atypical oxy-fuel burner 10 in the specific embodiment under description.

1. In a furnace for processing metal bearing charge, having a shaftportion, a hearth portion, means for introducing a composite of saidcharge and coke into the shaft of said furnace, means for sustaining aprocess including combustion and chemical action in the hearth portionof said furnace, and means for drawing the molten metal product and slagformed as a result of said process, the improvement comprising: aplurality of oxy-fuel burners interposed through tuyeres of said furnaceand directed toward the hearth portion of said furnace, a source ofcommercially pure oxygen and a source of hydrocarbon fluid fuel, each ofsaid burners comprising a plurality of separate channels for highvelocity streams respectively of the pure oxygen and fluid fuel, saidchannels terminating in a nozzle constructed to emit a plurality of highvelocity jets of oxygen surrounding at least one jet of said hydrocarbonfuel, means for post-mixing said jets to obtain a turbulent mixture atthe tips of said burners for producing a single homogeneous, highvelocity, high temperature flame in an established combustion zone andwhich remains seated at each nozzle, said flame having a temperaturewithin the range of from 3,000* to 5,000* F and having a flame velocityof from 500 to 3,500 feet per second at a flame temperature within saidaforementioned temperature range, a delivery system for respectivelyconnEcting said oxygen and fuel sources to said separate channels ineach of said burners, and means for supplying said tuyeres from a blastmain with air to produce an air blast velocity in the tuyeres in therange of from 150 to 1,000 feet per second during the operation of saidburners, the velocity of the flame of each of said burners at leastexceeding the velocity of said blasts of air in said tuyeres, wherebythe charge-to-coke ratio is substantially increased in said furnaceduring said process.
 2. A furnace in accordance with claim 1 whereinsaid burners are of the form of self-atomizing tip mixers, eachcomprising an axially-disposed oil channel terminating at the nozzle ina central vent comprising a relatively narrow neck, and wherein saidnozzle includes in addition a plurality of oxygen vents disposed in acircular array substantially concentric with said central oil vent.
 3. Afurnace in accordance with claim 1 wherein said fuel comprises aprincipal component of natural gas and said burners are of the form ofrocket burners each comprising a bundle of gas channels terminating in aplurality of vents in circular array substantially centered in saidnozzle, said nozzle including a plurality of oxygen vents adjacent toand symmetrically spaced with reference to said gas vents.
 4. Thecombination in accordance with claim 3 wherein said burners and saiddelivery system are constructed and arranged to sustain at each of saidnozzles flame velocities of between 1,000 and 3,500 feet per second at aflame temperature within the range 3,200* to 5,000* F.
 5. A furnace inaccordance with claim 3 wherein said fuel comprises principal componentsof both gas and oil, and said rocket burners include a single axiallydisposed oil channel terminating in a central oil vent at said nozzle,in addition to said gas and oxygen vents which are symmetricallydisposed relative to said oil vent.
 6. The combination in accordancewith claim 1 wherein said furnace is surrounded by a blast main, pumpingmeans and a conduit connected to said blast main for generating a highvelocity stream of air in said blast main, and a plurality of tuyeresare interposed in the wall of said furnace adjacent said hearth portionand connected to receive a portion of the high velocity air stream fromsaid blast main, said burners being interposed in at least a portion ofsaid tuyeres and surrounded by said high velocity air, and wherein saidtuyeres include water cooling means, and wherein the nozzle of each ofsaid burners is recessed in said respective tuyeres to the exteriorlimit of said water cooling means in said tuyeres.
 7. The combination inaccordance with claim 1 wherein said furnace is a water-cooled iron-oresmelting blast furnace having a circular wall of refractory materialsurrounding said hearth portion, said tuyeres, including water coolingmeans therefor, being interposed in said walls in circular array in aplane adjacent to and slightly above said hearth portion, oxy-fuelburners extending into said tuyeres and adapted to establish flamestability within respective tuyeres at fuel and oxygen velocitiesranging from 10 feet per second to supersonic velocities.
 8. Thecombination in accordance with claim 1 wherein said furnace is a blastfurnace of rectangular plan comprising substantially plane metal wallsfor processing ore containing a principal component of a metal selectedfrom the group consisting of lead and antimony, at least one pair ofsaid walls including a plurality of tuyeres disposed in a plane adjacentto and slightly above said hearth portion, said tuyeres substantiallyaligned and facing each other, said burners being interposed into atleast a portion of said tuyeres on opposite sides of said furnace anddirected toward said hearth portion.